diff --git a/synapse/storage/account_data.py b/synapse/storage/account_data.py
index 625d062eb..b8387fc50 100644
--- a/synapse/storage/account_data.py
+++ b/synapse/storage/account_data.py
@@ -157,6 +157,10 @@ class AccountDataStore(SQLBaseStore):
                     "content": content_json,
                 }
             )
+            txn.call_after(
+                self._account_data_stream_cache.entity_has_changed,
+                user_id, next_id,
+            )
             self._update_max_stream_id(txn, next_id)
 
         with (yield self._account_data_id_gen.get_next(self)) as next_id:
diff --git a/synapse/util/caches/stream_change_cache.py b/synapse/util/caches/stream_change_cache.py
index 891cb619f..b37f1c072 100644
--- a/synapse/util/caches/stream_change_cache.py
+++ b/synapse/util/caches/stream_change_cache.py
@@ -52,15 +52,10 @@ class StreamChangeCache(object):
             cache_counter.inc_misses(self.name)
             return True
 
-        if stream_pos == self._earliest_known_stream_pos:
-            # If the same as the earliest key, assume nothing has changed.
-            cache_counter.inc_hits(self.name)
-            return False
-
         latest_entity_change_pos = self._entity_to_key.get(entity, None)
         if latest_entity_change_pos is None:
-            cache_counter.inc_misses(self.name)
-            return True
+            cache_counter.inc_hits(self.name)
+            return False
 
         if stream_pos < latest_entity_change_pos:
             cache_counter.inc_misses(self.name)
@@ -98,7 +93,7 @@ class StreamChangeCache(object):
 
         if stream_pos > self._earliest_known_stream_pos:
             old_pos = self._entity_to_key.get(entity, None)
-            if old_pos:
+            if old_pos is not None:
                 stream_pos = max(stream_pos, old_pos)
                 self._cache.pop(old_pos, None)
             self._cache[stream_pos] = entity